A Model of Linear Arm Movements with Preview Constraints

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Abstract
This study extends Fitts's law for linear and serial arm movements to incorporate constraints on the preview (distance) for each movement. A simple first-order linear model relating mean movement time to Fitts's index of difficulty (ID) variable and a preview-constraint ID variable was found to explain 92% of the variation in movement time. The results, which were based on a sample of 12Ss, showed that the preview-constraint variable contributed more to the movement time than did Fitts's ID variable. The information rate generated was 6·2 bits/sec, which was about half that produced by similar tasks involving no preview constraints and about 60% higher than that produced by rotary arm movements with preview constraints. The relatively large error rates generated were predominantly overshoot errors. The highest error rates occurred for the more difficult tasks as reflected by large ID values. Both movement times, error rates and parameter estimates showed large variations between individual Ss. The mean movement times across Ss were considerably higher than predetermined motion-time systems predictions.

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